Project Information

Summary:

Currently, fungicides play an important role in fresh market tomato production and are applied on nearly 100% of the tomato hectarage in the north central production region. Most growers initiate fungicide sprays when fruit first set and apply subsequent sprays every 7 to 14 days even if there is no disease risk, resulting in up to 12 or more applications each season.

Recent concerns about fungicide residues on food have affected midwestern tomato production signficantly, which has received attention because of heavy fungicidal use in disease control programs in this region. A disease forecasting system that reduces fungicide use without increasing disease-related losses has been implemented successfully in the Midwest and Ontario for processing tomatoes. However, this forecasting system has not been evaluated for its applicability for fresh market tomato production in the Midwest. Fresh market tomatoes are thin skinned compared to processing tomatoes and are therefore more susceptble to fruit rots. Also, fresh market tomatoes are picked in multiple harvests and graded for blemishes whereas processing fruit are harvested once by machine and not graded on appearance. In this study, fungicide sprays were reduced substantially (a minimum of 36%) by making applications according to a disease forecasting system (TOM-CAST) with fungicide sprays triggered by cumulative disease severity values of 13 to 18. Fungicide sprays applied according to the disease forecaster provided control comparable to that obtained with a calendarized conventional spray program. Depending on the fungicide used, $56 to $150/acre savings were realized with use of this forecasting system. Zone tillage allowed persistence of surface rye residue to limit soil and wind erosion and wind-whipping damage to plants. Conservation tillage, use of cover crops and reduced fungicide inputs have considerable benefit for soil health, soil quality, environmental quality, and overall long-term sustainability of field productivity and profitability.

Project Objectives:

Evaluate the potential of integrated disease management practices including a disease forecasting model and reduced tillage for the control of early blight, anthracnose, and soil rot in a fresh market tomato system that includes rotation to cucumber, use of rye cover crops, and a mustard green manure.

Research

Materials and methods:

Location and design of field experiments. Field experiments were conducted on a Spinks sandy loam (87.4% sand, 6.0% silt, and 6.6% clay) at the Southwest Michigan Research and Extension Center near Niles, Michigan. A split design was used with four replications arranged in randomized complete blocks. Main plots were divided into two 12 x 42 m subplots to investigate the influence of tillage (conventional vs. zone tillage). Each subplot was divided into seven 12 x 6 m sub-subplots to investigate fungicide treatments (for a 2x2x7 factorial design (n=112)). Plots planted to tomato consisted of four rows of fresh market ‘Pik Rite’ tomatoes. Cucumber ‘Flurry’ was used in rotation.

Tomato seedlings were grown in a commercial greenhouse in 288-cell flats for four to five weeks. Seedlings were transplanted in late May using a conventional single-row transplanter with double disk openers and a wide rubber drive. Seedlings were spaced 0.3 m, on 1.5-m centers. Overhead sprinkler irrigation was applied as needed.

In the fall prior to the initiation of the study, the field plot was plowed and drilled to mustard. Mustard was chosen for its potential to reduce inoculum of plant pathogens, grow rapidly, and protect the light sandy soils from erosion, and retain nutrients that otherwise might leach from the soil.

Main plots: Tillage system. Conventional tillage (CT) was one treatment and consisted of spring moldboard plowing to a depth of 20-23 cm when the overwintered rye was 15-20 cm tall. Up to two additional field passes with a disk, drag, or both were employed for field preparation before planting. After each tomato harvest, plots were conventionally tilled and rye seeded. Zone tillage (ZT) was used as a second tillage treatment. In early spring (late March to early April) of each year, paraquat (Gramoxone) was applied to the overwintered rye in strips 0.46 m wide on 1.5-m (row) centers to minimize rye biomass where tomato or cucumber plants were to be established. The interrow rye was desiccated with paraquat when it reached a height of 1 to 1.2 m.

In ZT plots each spring, the Tye paratill was set to fracture the soil to approximately 35 cm deep with minor surface disturbance and no soil inversion. Zone tillage was performed on the exact same row center where tomato plants once stood and tomato or cucumber were to be planted.

Subplots: Fungicide treatment. Fungicide treatments included unsprayed, sprayed weekly, or sprayed at intervals according to a disease forecasting model, TOM-CAST, that calculates a daily disease severity value (DSV) based on the average temperature during hours when leaves are wet. Hourly mean temperature and leaf wetness were recorded using the Omnidata model DP223 temperature and leaf wetness recorder. TOM-CAST calls for an initial spray on 11 July or earlier is DSVs reach a threshold of 35 for seedlings planted prior to 23 May and 45 for seedlings planted after 23 May accumulation of every 13 or 18 DSVs (1995) or every 10 or 13 DSVs (1996). The fungicides Bravo 720 (chlorothalonil) or Penncozeb (ethylene-bis-dithiocarbamate) were used throughout the study at the full recommended rate.

Research results and discussion:

In 1995, fungicides were applied weekly (16 sprays) or at TOM-CAST disease severity values (DSV) of 13 (9 sprays) or 18 (6 sprays). Fruit were harvested at the breaker stage each week for a 5-week duration and evaluated for the presence of fruit rot including early blight (Alternari solani), soil rot (Rhizoctonia solani), and/or anthracnose (Colletotrichum coccodes).

In the unsprayed strip tillage plots, an average of 36.4% of the fruit showed symptoms of fruit rot. When Penncozeb (3 pt./A) was applied, average fruit rot incidence was 8.1% (7-day intervals), 9.5% (DSV=13), and 11.8% (DSV=18). When Bravo 720 6F (3 pt./A) was applied, the average fruit rot incidence was 4.8% (7-day intervals), 4.0% (DSV=13), and 7.8% (DSV=18). In the conventional tillage plots, a season average of 30.4% of the fruit harvested from the unsprayed control plot were infected with fungal fruit molds. When Penncozeb (3 pt./A) was applied, average fruit rot incidence was 9.2% (7-day intervals), 8.3% (DSV=13), and 8.0% (DSV=18). When Bravo 720 6F (3 pt./A) was applied at 7-day intervals or according to DSVs of 13 and 18, average fruit rot incidence was 5.5% regardless of treatment.

In 1996, fungicides were applied weekly (14 sprays) or at TOM-CAST disease severity values (DSV) of 10 (12 sprays) or 13 (9 sprays). Fruit were harvested at the breaker stage each week for a 5-week duration and evaluated for the presence of fruit rot including early blight, soil rot, and/or anthracnose. To evaluate the potential of latent fruit infections, harvested fruit were held for one week to allow ripening and re-evaluated for fruit rots. Data presented in this report represent the cumulative fruit rot observed. In the unsprayed strip tillage plots, an average of 52.7% of the fruit showed symptoms of fruit rot. When Penncozeb (3 pt./A) was applied, average fruit rot incidence was 27.1% (7-day intervals), 29.0% (DSV=10), and 26.6% (DSV=13). When Bravo 720 6F (3 pt./A) was applied, the average fruit rot incidence was 23.8% (7-day intervals), 25.4% (DSV=10), and 25.1% (DSV=13). In the conventional tillage plots, a season average of 50.0% of the fruit harvested from the unsprayed control plot were infected with fungal fruit molds. When Penncozeb (3 pt./A) was applied, average fruit rot incidence was 21.5% (7-day intervals), 19.7% (DSV=10), and 23.9% (DSV=13). When Bravo 720 6F (3 pt./A) was applied, fruit rot incidence was 14.4% (7-day intervals), 16.2% (DSV=10), and 18.3% (DSV=13).

In 1995, tillage did not appear to impact the level of fruit mold observed. The TOM-CAST disease forecasting system utilized DSV thresholds of 13 or 18 to trigger a fungicide spray and provided disease control comparable to the conventional 7-day application schedule while saving a minimum of 7 sprays (44% reduction). To assure growers that more conservative DSV thresholds were unnecessary, the 1996 experiment implemented DSV thresholds of 10 and 13 and fruit were held for re-evaluation following ripening to assess latent infections. Differences between tillage treatments and among fungicide timing treatments were not observed. While the most conservative spray threshold of DSV=10 saved only 2 sprays (14% reduction), the spray threshold of DSV=13 saved 5 sprays (36% reduction) in comparison to the conventional spray program.

In summary, the data suggest that fungicide sprays can be reduced substantially (a minimum of 36%) by making applications according to a disease forecasting system (TOM-CAST) using DSV=13-18, and still provide control comparable to that obtained with calendarized conventional spray programs.

Research conclusions:

Integrated control of early blight, anthracnose, and soil rot with reduced fungicide input was possible in a fresh market tomato production system. Conservation tillage, use of cover crops and reduced fungicide inputs have considerable benefit for soil health, soil quality, environmental quality, and overall long-term sustainability of field level productivity and profitability. In this study, substantial benefit in terms of reduced soil erosion and wind damage to plants were achieved with zone tillage. Soil maintenance qualities of the rye residue were qualitatively observed after several rain storms. Soil erosion was obvious in conventionally tilled plots compared to zone tillage plots. The potential of reducing wind erosion of soil and protecting plants from excessive winds was observed. Following a severe sand storm, tomato plants were wind whipped and tilted toward the soil surface in conventionally tilled plots. Plants in the zone tillage plots remained upright. Zone tillage allowed persistence of surface rye residue to limit soil and wind erosion and wind-whipping damage to plants.

Zone tillage holds considerable promise for tomato production systems. A reduced fungicide program was effectively incorporated into the production system and was successful, in part, due to the integrative impacts of cultural and chemical based control strategies.

However, a higher level of management was required when both strategies were combined. This combination makes the production system more dependent on an enhanced knowledge base as opposed to production inputs. This will prove to be a challenge for the farm manager.

Ultimately, integrated management is dependent on the ability of the farm manager to integrate available knowledge into a working production system. However, private and public research and extension must provide a framework and knowledge resource base from which the farm manager can draw. Currently, in tomato production systems, the knowledge base lags behind the stimulus to change production systems.

Currently, fungicides are applied on nearly 100% of tomato hectarage in the North Central production region. Most growers initiate fungicide sprays when fruit first set and apply subsequent sprays every 7 to 14 days even if there is no disease risk, resulting in up to 12 or more applications each season. Recent research suggests that a reduced number of fungicide applications can be used when timed according to environmental conditions favorable for disease development. Disease forecasting systems are designed to determine the need for the initiation and/or timing of subsequent fungicide applications for the purpose of reducing disease incidence and efficient use of resources. This approach is more compatible with goals of a sustainable agriculture.

Economic Analysis

The total cost of each fungicide program was calculated by multiplying the number of applications by cost ($15.00/acre/application for Bravo 720; $8.00/acre/application for Penncozeb). In 1995, 7 sprays were saved when the disease forecaster TOM-CAST was used with a spray threshold of 13 DSVs. This translates to a savings of $105 or $56/acre depending on whether Bravo 720 or Penncozeb would be used, respectively. In a disease management system whereby the more liberal spray threshold of 18 DSV was used, a total of 10 sprays were saved in 1995 resulting in a financial savings of $150 or $80/acre for Bravo 720 or Penncozeb, respectively. In 1996, two fungicide applications were avoided using a disease forecasting system with a DSV of 10 resulting in savings of $30 and $15/acre for Bravo 720 or Penncozeb, respectively. When using a DSV of 13, 5 fungicide sprays were avoided and produced a savings of $75 or $56/acre for Bravo 720 and Penncozeb, respectively. Based on the data, there was no risk associated with adoption of this particular disease forecasting program. The potential to save fungicide sprays and thereby realize financial savings is dependent on the yearly environmental conditions.

Farmer Adoption

Approximately 60 growers were in attendance at a Michigan State University extension sponsored meeting held in Benton Harbor, MI where the theme of the meeting was integrated pest management. Weekly DSVs of the forecasting system utilized in the research project were reported to a minimum of 300 growers via a statewide newsletter published by Michigan State University extension. Also, updates were provided on the number of fungicide sprays that were saved as a result of using the disease forecasting system.

Feedback from these extension activities indicates that growers are still skeptical of disease forecasting systems. Now that the spray thresholds have been determined for fresh market tomatoes, demonstration plots need to be established on commercial grower sites to encourage adoption of disease forecasting as a management tool.

Additional opportunities to discuss research results and implications for implementation exist at various regional grower meetings in 1997. The principle investigator of this project has a 60% extension appointment and is routinely requested to speak with growers and agribusiness representatives regarding emerging disease management strategies. These speaking requests provide ample opportunity to introduce disease forecasting as a powerful tool in managing diseases in tomatoes.

Involvement of Other Audiences

The results of this research were presented during a Michigan State University extension sponsored meeting held in Benton Harbor, MI in 1995. Approximately 60 growers were in attendance and the theme of the meeting was integrated pest management.

Weekly updates of the research project including cumulative DSVs were reported to a minimum of 300 growers via a statewide newsletter published by Michigan State University extension. Additional opportunities to discuss research results and implications for implementation exist at various regional grower meetings in 1997. The principle investigator of this project has a 60% extension appointment and is routinely requested to speak with growers and agribusiness regarding emerging disease management strategies. These speaking requests provide ample opportunity to introduce disease forecasting as a powerful tool in managing diseases in tomatoes.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

The results of this research were presented during a Michigan State University extension sponsored meeting held in Benton Harbor, MI in 1995. Approximately 60 growers were in attendance and the theme of the meeting was integrated pest management.

Weekly updates of the research project including cumulative DSVs were reported to a minimum of 300 growers via a statewide newsletter published by Michigan State University extension. Additional opportunities to discuss research results and implications for implementation exist at various regional grower meetings in 1997. The principle investigator of this project has a 60% extension appointment and is routinely requested to speak with growers and agribusiness regarding emerging disease management strategies. These speaking requests provide ample opportunity to introduce disease forecasting as a powerful tool in managing diseases in tomatoes.

The results of this study will be included in a graduate student’s M.S. thesis and will be suitable for publication in “Plant Disease” which is a refereed journal of the American Phytopathological Society. This journal is widely read by those with extension appointments who have the potential to significantly impact disease management practices within the agricultural community.

Project Outcomes

Recommendations:

Areas needing additional study

Additional efforts need to be made in evaluating the initiation of the disease forecasting system TOM-CAST. It is possible that delaying the onset of the forecasting system would not negatively impact fruit quality but would further reduce fungicide applications.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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